1. Field of the Invention
The present invention relates to an electronic apparatus including a printed circuit board having a wiring pattern of a differentially operated signal line.
2. Description of the Related Art
Conventional differential transmission paths mounted on a printed circuit board included in an electronic apparatus comprise differential transmission paths of USB (Universal Serial Bus) standard or HDMI (High-Definition Multimedia Interface) standard. For such differential transmission paths, each characteristic impedance of a pair of differential transmission paths needs to be uniform at a value determined by each standard.
Meanwhile, with increasing performance and added value of an electronic apparatus, a printed circuit board including an electronic circuit for realizing higher performance and added value has achieved higher speed of a circuit operation or higher density of signal lines (wiring pattern). With increasing speed of the circuit operation, a frequency of a clock line increases, which may cause unnecessary radiation noises. Also, with increasing signal lines, signal lines that function as noise sources are arranged adjacent to each other, which may cause crosstalk (interference of noises). This has made it difficult to obtain a uniform characteristic impedance.
A technique on a pattern layout has been proposed for reducing unnecessary radiation noises of a differential transmission path as described above, and preventing crosstalk with other signals (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 2001-267701).
However, since an electronic circuit having a differential transmission path of USB standard or HDMI standard has been heretofore independently mounted on a printed circuit board, it has been only necessary to note a pattern layout associated with a pair of differential transmission paths and other signal lines. However, with increasing performance or added value of an electronic apparatus, differential transmission paths of a plurality of standards have been mounted on the same printed circuit board, and thus there is a problem in which interference between differential transmission paths having characteristic impedances of different values occurs.